This looks really cool. What bothers me (or am unable to imagine how it would work) is multiplicity. Allow me to elaborate.In my Thunderbird, I have 6 email accounts, each with multiple folders (inbox, sent, deleted, archive). That itself is just two layers of variation. While multiple folders can be written next to where it says "inbox", we must have a way to have multiple accounts as well.In addition, how would things such as multiple messages be handled? Would they open in separate boxes, or in tabs / pivots, or not at all? Having multiple messages open at the same time is important.Finally, we would need a search bar, at least in the left window. In the right (message) pane, one could hit F3 or Ctrl+F to bring it forward, but it should be readily visible in the left window.